Many modern medical procedures use tubing sets of varying complexity to withdraw fluid from a patient, or to administer fluid to a patient, or to do both. One example of such a procedure is hemodialysis. In hemodialysis, the patient's blood is cleansed by drawing it out of the patient through a blood access site, typically via a catheter, and passing it through an artificial kidney (often called a “dialyzer”). The artificial kidney includes a semi-permeable membrane which removes impurities and toxins by a process of diffusion. The purified blood is then returned to the patient. An extracorporeal circuit including a pump and hemodialysis tubing set is typically used to transport the blood between the blood access site and the artificial kidney.
Many of the tubing sets used in medical procedures involving extracorporeal treatment of fluid, such as hemodialysis, are configured so that fluid can flow through the system in a desired direction during the medical procedure. A pumping device can be used to control the fluid flow rate in the system. In hemodialysis, for example, a peristaltic pump is typically used to draw blood from the patient and move the blood through the tubing set during the treatment procedure. During hemodialysis, blood is initially drawn from the patient's blood access (e.g., a vein or an artery, but more typically an arteriovenous graft or fistula) and flows through a series of connected tubing segments to the artificial kidney for cleansing. After passing through the artificial kidney, the blood then flows through other tubing segments that return the blood to the patient. Thus, there is generally a continuous circuit of blood flowing from the patient, through the artificial kidney, and then back to the patient during treatment.
During hemodialysis, blood is generally drawn from an upstream position in the blood access and then returned to a downstream position in the blood access. However, it has been found to be advantageous, for limited time periods, to reverse the direction that blood is received from and returned to the patient during hemodialysis. When the blood flow is reversed, blood is initially drawn from a downstream position in the blood access. The blood then flows through tubing segments to the artificial kidney for treatment before it is returned to the upstream position in the blood access. Typically this procedure is carried out by trained clinical personnel, e.g., dialysis clinicians. When the blood flow is reversed, any of various parameters, such as blood access flow rate, can be measured or derived from measurements. The data can provide useful information about the patient's condition and the effectiveness of the treatment. For example, practitioners can use information gathered during periods of reversed blood flow to evaluate the condition of the blood access, to get advanced warning on other health problems, such as access restrictions, and to prescribe preventive measures, such as blood access revision or replacements, which are generally needed after a few years of continuous dialysis.